Messages in this thread | | | From | Michael Buesch <> | Subject | Re: [PATCH 1/6] kernel: add clamp(), clamp_t() and clamp_val() macros | Date | Wed, 12 Mar 2008 18:20:14 +0100 |
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On Wednesday 12 March 2008 17:54:26 Harvey Harrison wrote: > On Wed, 2008-03-12 at 16:13 +0100, Michael Buesch wrote: > > So why not call it clamp_const()? > > One could even use __builtin_constant_p() and make clamp() use > > either clamp_const() or clamp_nonconst() from above automagically. > > I'd prefer that. > > Did you mean something like this? No more clamp_val, just clamp and > clamp_t. clamp_t forces all the types, clamp looks at the min and max > args, and if they are constants, uses the type of val instead. If not > a constant, the strict typechecking is done.
> +#define clamp(val, min, max) ({ \ > + typeof(val) __val = (val); \ > + \ > + if (__builtin_constant_p(min)) { \ > + typeof(val) __min = (min); \ > + __val = __val < __min ? __min: __val; \ > + } else { \ > + typeof(min) __min = (min); \ > + (void) (&__val == &__min); \ > + __val = __val < __min ? __min: __val; \ > + } \ > + \ > + if (__builtin_constant_p(max)) { \ > + typeof(val) __max = (max); \ > + __val > __max ? __max: __val; \ > + } else { \ > + typeof(max) __max = (max); \ > + (void) (&__val == &__max); \ > + __val > __max ? __max: __val; \ > + } })
Yeah, something like that. Does returning of the value work over an indentation level, too? I dunno this detail of the language. But I'd prefer the following for readability anyway:
+ if (__builtin_constant_p(max)) { \ + typeof(val) __max = (max); \ + __val = __val > __max ? __max: __val; \ + } else { \ + typeof(max) __max = (max); \ + (void) (&__val == &__max); \ + __val = __val > __max ? __max: __val; \ + } + __val; })
Probably you can also only put the pointer check into the constant check:
+#define clamp(val, min, max) ({ \ + typeof(val) __val = (val); \ + typeof(min) __min = (min); \ + typeof(max) __max = (max); \ + if (!__builtin_constant_p(min)) \ + (void) (&__val == &__min); \ + __val = __val < __min ? __min: __val; \ + if (!__builtin_constant_p(max)) \ + (void) (&__val == &__max); \ + __val = __val > __max ? __max: __val; \ + __val; })
But it seems that this evaluates the arguments twice, so my idea turns out to be not too good anyway. hm..
-- Greetings Michael.
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